A four-terminal network can be wired 1) asymmetrically/asymmetrically or 2) symmetrically/symmetrically. It is also possible to wire a four-terminal network as a balun, i.e., 3) asymmetrically/symmetrically.
A duplexer is known from the publication US 2001/0013815 A1 in which a balun is realized in the receive path in a filter by a DMS track (DMS=double acoustic mode SAW, SAW=surface acoustic wave) which is connected to series resonators. The series resonators are formed as SAW resonators. The filter structures used in the duplexer are all constructed in one technology (SAW).
A duplexer with a receive path is known from the publication US 2002/0140520 A1. A receive filter is arranged therein in which a ladder-type arrangement is connected on the output side to a balun or an additional element for symmetrization of the ladder-type arrangement. The balun can be realized by LC components or by an arrangement of SAW or BAW resonators (BAW=bulk acoustic wave). Individual SAW resonators, each arranged in a track of its own, or BAW resonators arranged side by side are not acoustically coupled to one another.
An electrical circuit that can be switched between at least two of the operating modes 1), 2) or 3) is disclosed.
In some embodiments, an electrical circuit includes an electric quadrupole that has two electrical ports, each having two terminals. At least one shunt arm that runs from a terminal of the first port to ground is provided in the circuit. A switching element (first switching element), by means of which the corresponding terminal can be placed at ground potential, is provided in the shunt arm.
In a preferred variant the circuit has a second shunt branch, which runs from one terminal of the second port to ground. A switching element (second switching element) is also arranged in the second shunt branch.
In case a switching element is short-circuited, the electrical port connected thereto is asymmetric. In the case of an open switching element, the port can be operated symmetrically.
The circuit has the advantage that the respective electrical port can be switched between symmetric and asymmetric operation. The switching can be open or short circuited for a long period by applying or omitting a control voltage. In case of a short circuited first and an open second switching element, a balun can be realized by the electrical circuit, making it being possible to forgo a special balun circuit.
The electric four-terminal network is, for instance, a filter, preferably a bandpass filter. The four-terminal network preferably has component structures operating with bulk or surface acoustic waves (e.g., SAW transducers or BAW resonators; SAW=surface acoustic wave; BAW=bulk acoustic wave). Several acoustically coupled and preferably galvanically separated BAW resonators can form a resonator unit. A resonator unit operating with SAW can have several SAW transducers.
In some embodiments the quadrupole has transducers operating with surface acoustic waves. Several, for example, two transducers associated with a resonator unit are acoustically coupled to one another and preferably electrically isolated from one another. The transducers are preferably arranged side by side in an acoustic track.
The BAW resonators arranged in a resonator unit can be situated in a resonator stack one above the other and acoustically coupled to one another via a partially acoustically transmissive coupling layer arranged between them. The BAW resonators can also be arranged side by side and acoustically coupled to one another via a lateral acoustic coupling. The resonator unit preferably comprises two resonators or transducers.
Each resonator or transducer of the resonator unit in one variant is arranged in a signal path of its own. In another variant, each resonator or transducer is connected to only one of the ports and arranged between two terminals of the first or second port.
The first and/or second switching element is, for example, a PIN diode, a field-effect transistor or a microelectromechanical switch (MEMS).
The invented circuit is preferably realized in a compact component. The component preferably has a multilayer substrate with several dielectric and/or semiconductive layers. Structured metallization layers that are electrically connected to the external terminals of the component by means of through-hole contacts, for instance, are arranged between the dielectric layers. A part of the circuit can be buried in the substrate or formed in the metal layers. The substrate has, among other things, external terminals that serve to control the first or second switching element.
The electric four-terminal network and the first or second switching element are preferably realized in a common substrate or arranged on a common substrate.
Electroacoustic structures of the electrical circuit are preferably arranged on the surface of the substrate. It is also possible to mount a chip with BAW or SAW structures on the substrate. This chip can be connected to the substrate by wire-bonding or by flip-chip technology.
In one variant the switching elements are realized in the interior of the substrate. In another variant the switching elements are mounted on top of the substrate.
The substrate preferably has ceramic layers as dielectric layers. The dielectric layers can also consist of a synthetic resin or an organic material. The substrate can have different types of dielectric or semiconductive layers arranged one above another (e.g., Si and SiO2).
The invention will be explained in detail below on the basis of embodiments and the associated figures. The figures show various embodiments of the invention on the basis of schematic representation not drawn to scale. Identical or identically acting parts are labeled with identical reference characters. Shown are: